Multiplex system



OV 3, 1942. o. T. FRANCIS MULTIPLEX SYSTEM Filed April 25, 1940 3 Sheets-Sheet 1 g mogxixw Nov. 3, 1942. Q. T. FRANCIS MULTIPLEX SYSTEM Filed April 25, 1940 3 Sheets-Sheet 2 M was ER I Nov. 3, 1942. x o. T. FRANCIS MULTIPLEX SYSTEM Filed April 25, 1940 3 Sheets-Sheet 3 WWZ 6A5 mscunnae- DEVICE Patented Nov. 3, 1942 UNITED STATES PATEN OFFICE MULTIPLEX SYSTEM Oliver '1. Francis, Renville, Minn. Application April 25, 1940, Serial No. 331,644

19 Claims.

This invention relates to multiplex systems on the time division basis, and more particularly to electronic commutators used at the transmitting and receiving stations, to means for shifting multiplex channels from one to another and to means for synchronizing said commutators.

This invention is a continuation in part of my copending application Ser. No. 281,965 filed June 29, 1939entitled "Electronic commutator."

In the above application a. synchronizing station separate from, and operating on a different frequency from the signal transmitting station was illustrated. It is an object of this invention to illustrate means whereby the synchronizing pulsesmay be sent out over the same channel as the signals are sent over. 1

In multiplex signal amplification comprising object of this invention to illustrate a multiplex system which is rendered secret by means of a random method of shifting said channels at the amplification of a series of pulsations of the same polarity, difficulty is experienced in amplifying the "square wave forms without undue distortion. Especially is this the case where the number of channels involved is large. The tails left on the signals by transformer, impedance, or even resistance condenser coupling are well known to those experimenting in these fields. Combinations of resistance and impedance coupling have given somewhat better results, but even here electrical "inertia" once introduced into a circuit is difilcult to compensate against. In U. 8. Patent No. 1,886,386 issued to me November 8, 1932, I illustrated a method of amplification whereby weak signals may be built up to any desired strength in a single'stage of amplification without the use of capacitive or inductive reactances. invention to illustrate how the system of amplification therein illustrated may be adapted to distortionless amplification oi the "square wave forms of multiplex systems and similar systems.

In multiplex systems the scanner voltages usually obtained irom three electrode gas discharge devices, is limited to 100 or 200 volts if any degree of linearity is to be preserved. The power obtainable from such circuits where the number of commutator units involved is large is limited.

It is an object of this invention to illustrate how the magnitude of this "sweep voltage may be increased to any desired degree by placing said gas discharge device in the input and output circuit of a thermionic tube, and placing a vacuum tube choke as the load of said thermionic tube. I

Multiplex signal communication is not a secret method of communication, since it may be picked up by anyone having similar apparatus. It is an It is an object of this frequent intervals.

With these and other objects in view the invention may be more readily understood by reference to the following description and drawings wherein:

Fig. 1 is a multiplex signal transmitter.

Fig. 2 is a multiplex signal receiver.

Fig. 3 is a modification of Fig. 1.

Referring to Fig. l, I is a grid controlled gas discharge device, the cathode of which is heated by an A battery 2, the grid of which is connected through a resistance 3 to a negative source or voltage 4, the cathode of gas device I being connected to 4 at a more positive potential to thereby place the desired negative potential on the grid of I. In parallel with I is a condenser 5. Device I is connected in the input and output circuit of thermionic grid controlled tube 6. The grid of 6 is connected'through a resistance I to a point on battery 4 more positive than the cathode of I to reduce the 1R drop across tube 8. The cathode of tube 5 is heated by an A battery 8. The anode of 8 is connected to source of voltage 9. In parallel with tubes I and 8, are connectedresistances III and II, which in turn are in parallel with small condensers I2 and I 3, I

which act to bypass high frequency transients.

In the output circuit of I and G is connected vacuum tube choke l4, the anode of which is connected to the positive terminal of battery 4, the cathode being heated by battery I 5, and connected through resistance IE to the negative terminal of battery 9. The grid of I4 is connected through resistance I! to a point on 9 more positive than its cathode to render the direct current voltage drop across I4 small.

Grid controlled thermionic tube I8, with its cathode heated by battery 2, and its anode connected through primary of transformer III to the positive terminal of battery 4, and its grid connected through resistance 20 to a negative point on battery 9 comprises a means for impressing synchronizing pulses on secondary 01' I9. One

terminal of secondary I9 is connected through a. resistance 2|, and rectifier tube 22, the filament of which is heated by battery 23, to ground. The other terminal of the secondary is connected to the other side of line 24.

Across battery 4 is a plurality of potentiometers comprising photo-electric cells 25, 26 and variable resistances 21, 28. Acr battery 9 is a 55 plurality of potentiometers comprising photophoto-electric cell 30 and resistance 32.

electric cells 23, 30 and variable resistances 3I, 32. Tape 33, which is illuminated by a source of light 34, controls the impedance or photo electric cells 25, 25, 23, 30 in the following manner.

Light from source 34 illuminates tape 33. On this tape are darkened strips 53, 54, 55, 65. Light from strip 53 is focused by lens system 53 through linear opening 58 in shield 51 onto photo-electric cell 25. Light from strip 54 is focused onto 25. Light from strip 55 is focused onto cell 23 and light from strip 55 is focused onto cell 30. Tape 33 is drawn over roller 52 in front of opening 58 by roller 5| which in turn is drawn by synchronous motor 50.

Two commutator tubes 35, 35 are shown in Fig. 1, and operate on the differential grid action described in my above referred to copending application. Tube 35 has two scanner grids one of which is connected through high resistance 31 to the connection between photo-electric cell 25 and variable resistance 21. The other scanner grid of tube 35 is connected through high resistance 33 to the connection between photo-electric cell 23 and variable resistance 3|. Similarly the scanner grids of tube 35 are connected through high resistance 33 to the connection between the photo-electric cell 25 and variable resistance 28, and through resistance 40 to a point between Once these variable resistances have been set at a desired" value it will be evident that the potential on the scanner grids of tubes 35, 35 will be controlled by the impedance of photo-electric cells 25, 25, 23, 30 which in turn is controlled by light reflected from various parts of film 33 onto these cells in a manner described above. It is therefore evident that the sequence of scanning tubes 35. 35 operability is controlled in accordance with secret tape'33.

The means for impressing signals on tubes 35, 35 comprises keys 4|, '42 connected to battery 43, to impress a positive potential on the third grids of 35, 35 toicounteract the effect or the normal negative bias impressed on these grids by C battery 44 through resistances 45, 45. The cathodes of 35, 35 are heated by battery 23. 4

The anodes of tubes 35, 35 are connected to the cathode of tube 45 in such a manner as to render their plate impedances common to the input and output circuits of amplifier three electrode tube 45, the cathode of 45 being heated by a battery 45. In the output circuit of tube 45 is connected vacuum tube choke 41 having its cathode heated by battery 55. Resistance 50 is common to the input and output circuits or 41. A high resistance 48 impresses a positive potential on grid of 41 through gas tube 43, which counteracts the'efiect of the normally high negative potential impressed on the grid of 41 by the IR drop through resistance 50, and thereby renders the direct current impedance of tube 41 small. Reference is made to my U. S. Patent No. 1,886,386 issued November 8, 1932, for further description of amplification produced by tubes such as 45, and 41. 4

The grid and cathode of amplifier 51 are connected across vacuum tube choke 41 in .a novel manner comprising a high resistance 5| and a vacuumtube grid leak 52. The plate of tube 45 is maintained at a much higher D. C. potential than required by grid of amplifier 51. The resistance 5| has a high impedance to D. C. currents while tube 52 has a low D. C. impedance depending on the point where its grid is connected to battery 55. Tube 52 on the other hand has an extremely high impedance to the flow of alternating current, this A. C. impedance being equal to the value of resistance 53 plus the product of the ohmic resistance of 53 and the mu of tube 52. It is therefore evident that the grid of 51 is maintained at its proper operating voltage by reason of the direct current IR drop through resistance 51, whereas substantially all or the A. C. generated across tube 41 is impressed on grid of 51. The resistance 53 is common to the anode and grid circuit of tube 52 and is connected through a proper biasing battery 55 to the cathode of tube 51, which cathode is in turn heated by battery 23. In the output circuit of tube 51 is load resistance 53, and voltage variations thereacross are passed on to a receiving station by means or lines 24, 53.

Fig. 2 illustrates a multiplex receiving station for receiving the signals sent out by transmitting station shown in Fig. 1. Synchronizing pulses received from transmitting station over lines 24, 53 are in the present instance of opposite polarlty to and greater in magnitude than the signal pulses so as to render a current to flow from 53 through resistance IOI, gas tube I02 back to line 24. The breakdown voltage of I02 is of much higher value than the signal pulses so that the signal pulses will not effect the bias of thermionic three electrode tub'e I05. A negative bias is placed on tube I05 by the synchronizing pulses. thereby causing a decrease in its plate current flowing from battery I03 through primary 0! transformer I04 to plate of the tube I05. The secondary of I04 is so poled that a positive surge of voltage is impressed 0n grid controlled gas discharge device I08, through resistance I01, thereby overcoming the eifect or the high negative bias impressed on I08 by battery II3. Gas device I03 then discharges condenser II 0. The

cathode of I03 is heated by battery I03 and is connected to a point on battery I I9 more positive than its control grid.

One plate of condenser H0 is connected to the cathode of three electrode thermionic tube H5. The other plate of condenser H0 is connected to the cathode of gas discharge device I08. The grid of tube II5 is connected to battery II3 through resistance ill to a point more positive than the cathode of I 08, to render the voltage drop across II5 small when condenser H0 is discharged through gas device I08. Since the condenser IIO is in the grid cathode circuit of tube II5, as the voltage builds up across this condenser a negative potential is impressed on grid of tube H5.

In the common output circuit of tube H5, and gas device I08 is connected a vacuum tube choke I28, of the three electrode high vacuum type. The anode of I23 is connected to the positive terminal of battery II3. Its cathode is heated by battery I52, and connected through variable resistance I23 to the negative terminal of battery H8. The grid of tube I28 is connected to battery II8 ata point more positive than its cathode, thereby rendering the plate impedance of tube I28 small when a small anode voltage is impressed thereon through tubes I08, I I5.

Across battery II3 are potentiometers com- I21 and variable resistances I24, I25. The impedance of these photo-electric cells is controlled by light reflected from tape I35 which is illumiasoopee nated by a source light I63. The movement of tape I36 is synchronized with the movement of tape 33 at the transmitting station by synchronous motor I33 driving rollers I34 and pulling tape I36 over roller I35. Light from the darkened portion I31 is focused through lens system I36 through linear opening I32 in shutter I3I onto photo-electric cell I22. Similarly the darkened portion I36 is focused on cell I23, and darkened portion I39, I46 are respectively focused on cells I26, I21. thereby rendering scanner tubes I42, I46 operable at difierent values of voltage existing across resistances I I3, I I4, which resistances are connected across the plate impedances of tubes II5, I68. Condensers III, II2 are shunted across these resistances to by-pass high frequency transients existing in the circuit.

The cathodes of scanner tubes I42, I46 are heated by battery I65 and connected to the center point of resistance I I3, I I4. One of the scanner grids of tubes I42 is connected through high resistance I to the cathode of photo-electric cells I22. The other scanner grid is connected through high resistance I56 to the cathode of photo-electric cell I26. Similarly one of the scanner grids of tube I46 is connected through resistance I49 to the cathode of cell I23, while the other scanner grid is connected through resis'tance II to cathode of cell I21.

The control grids of tubes I42, I46 are connected in parallel to line 24, through resistance I41, a gas regulator tube I48 in parallel with resistance 'I53 and battery I66, regulating the magnitude of this voltage to a predetermined limit.

In the output circuit of tubes I 42, I46 is battery I63, resistance I45 and their respective loads I43, I44, here shown in theiorm of neon lamps.

In operation when the key controlling one of the commutator tubes is closed at the transmitting station a signal is sent out during a portion of the time interval between synchronizing pulses, which portion is variable in accordance with the record on tape 33. This signal appears at the receiving station in its corresponding receiving unit. which unit is operative during the same portion of said time interval as its corresponding commutator tube at the transmitting station and variable in accordance with secret tape I36 in synchronism with variations in said transmitting station.

The means for maintaining synchronism are shown as synchronous motors. Where alternating current from the same source is available such method of maintaining synchronism between the movement of tape 33 and I 36 is ideal. Where currents from a single source are not available at the transmitting and receiving stations other known methods may be resorted to, such as the synchronously driven magnets, which have been used in driving the mechanical commutators of multiplex telegraphy for many years, or synchronized clock mechanisms may be used. It is therefore not desired to limit the synchronous tape driving mechanism of the transmitting and receiving stations to the synchronous motors described. I p

The circuits shown in Figs. 1 and 2 each require three sources of high voltage supply. This adds weight to the equipment. As two of these sources are not. at ground potential, but vary from ground potential as the voltage across the.

gas discharge device varies, undesirable -fransients are introduced into the circuit.

shows how these sources of high voltage may be obtained from a single supply at ground potential and thereby make possible simplification of circuit arrangement.

5 Referring to Fig. 3, batteries MI, 262, con- 'stitute a single source of voltage supply. The scanner voltage generating circuit may be traced as follows: positive terminal of battery 26I, vacuum tube choke 261, gas discharge device 2I6,

1o biasing resistor 2I4, vacuum tube choke 268, battery 262. Vacuum tube choke 261 is a high vacuum three electrode tube having its filament heated by battery 2I6, a resistance 269 common to its plate and grid circuits, and C-battery 266 5 poled to place a'positive potential on its grid to render its impedance low to D. C. currents.

Vacuum tube choke 263 similarly is a three electrode high vacuum tube having its filament heated by battery 2I2, resistance 2 being common to its plate and grid circuits, and its grid connected to battery 262 at a point more positive than its filament to render its D. C. impedance small. I

Tube 2I6 is a grid controlled gas discharge device, its filament being heated by battery 2" and connected to the positive terminal of biasing resistance 2I4. Its grid is connected through resistance 2I5 to a point on biasing resistance 2I4 more negative than its filament. Condenser 265 in parallel with transient by-pass condensers 126:, 264 is connected in parallel with device One scanner tube 223, with its filament heated by battery 224, is shown. Its anode current is supplied through load resistance 2-22, the signal is impressed thereon by placing a positive voltage on its signal grid from battery 26L One of the scanner grids of tube 223 is connectedthrough high resistance 225 across vacuum tube choke 261 through a source of biasing voltage ccnsisting oi resistance 22I in series with vacuum tube choke 226. The other scanner grid of tube 223 is connected through resistance 226 to biasing resistance 2I4, which is in parallel with filter condenser 213 of high capacity.

Vacuum tube choke 226 is a three electrode vacuum tube with cathode heated by battery 221 and connected through resistance 2I9 to the negative terminal of battery 262. The control electrode of tube 226 is connected through resistance 2"! to a point on battery 262 more positive than its filament to render the D. C. impedance of tube 226 small.

While I have illustrated one method of syn- 5 chronized channel shifting arrangement in accordance with a secret record at a transmitting and receiving station,

be used with a variety of electronic commutators without departing from the scope of my invention. My invention is to be limited in scope only by prion-attend as described in the fol lowing claims.-

What is claimed is: 1. In a multiplex time munication systein; a transmitting station, a plurality of sourcesflof signals at said transmitting station, means" for, producing synchronizing pulses at a predetermined-time interval, means a for transmitting said signals from one of said sourcesdurin portion of said time interval, m'eanssfieri' iiting the portion 01 said time intergaketiming which said signals from said nne'source are transmitted to other portions of said time interval, in accordance with a ran- Fig. 3 dom record, a receiving station, a plurality or various other means may division signal com- I signal receiving devices at said receiving station, means for impressing said signals from said one of said transmitting means on a corresponding one of said receiving devices during said one por tion of said time interval, and means for shifting the portion of said time interval during which said receiving device receives signals in synchronism with said shifting of said one of said transmitting means, said last mentioned means comprising a second record similar to said first record at said receiving station, and means for synchronizing the movements 01 said records at said transmitting and receiving stations.

2. In a signalling system, a transmitting station, a, vacuum tube having an input and an output circuit at said station, cyclically operable signal generating elements connected in parallel in said input and said output circuit, a load in said output circuit, a receiving station, cyclically operable signal receiving elements at said receiving station, means i'or synchronizing said signal generating elements with said signal receiving elements and means for applying voltages across said load produced by one of said signal generating elements to a corresponding one of said signal receiving elements.

3. In a signalling system, a transmitting station, a vacuum tube amplifier having an anode, a cathode, and 9, control electrode at said station, cyclically operable signal generating elements connected in parallel in the circuit of leak tube being connected to said filament through a resistance common to the anode and control electrode circuit of said grid leak tube, a receiving station, cyclically operable signal receiving elements at said receiving station, means for synchronizing said signal generating elements with said signal receiving elements, and means for applying voltage variations across said load in said circuit of said plate of said second amplifier, produced by one of said signal generating elements, to a corresponding one, of said signal receiving elements.

4. In a signalling system, a transmitting station, a plurality of signal generating elements at said station, a scanner voltage source, comprising a vacuum tube having an input and an output circuit, a generator of a variable voltage connected in said input and said output circuit, a load connected in said output circuit, means for rendering said signal generating elements sequentially operable as said voltage across said load varies, a receiving station, cyclically operable receiving elements at said receiving station, means for synchronizing said signal generating elements with said signal receiving elements, and means for applying signal produced by said generating elements to corresponding ones of said receiving elements.

5. In a signalling system, a transmitting station, cyclically operable signal generating elements at said station, a receiving station, cyclically operable signal receiving elements at said receiving station, means for synchronizing said generating elements with said receiving elements, means for synchronously generating sequence controlling voltages at each of said stations, and means for synchronously changing the sequence of operability of said generating elements and said receiving elements to a new sequence with said sequence controlling voltages, said voltage generating means comprising similar photoelectric records at each of said stations, and means for synchronously varying the magnitude of said voltages generated at each of said stations in accordance with light variations synchronously produced at each of said stations by successive corresponding elemental areas of said records.

6. In a signalling system, cyclically operable transmitting elements, cyclically operable receiving elements, means for synchronizing said transmitting elements with said receiving elements, a photoelectric record, means for controlling the sequence of operability of one of said transmitting elements with light variations produced by successive elemental areas of said record, and a second photoelectric record for controlling the sequence of operability of one of said receiving elements in synchronism with said one of said transmitting elements, by light variations produced by corresponding successive elemental areas 01' said second record.

7. In a time division multiplex signaling system, an electronic commutator comprising a plurality of commutator unit vacuum tubes, a generator of a variable current, said generator comprising a vacuum tube having an input and output circuit, means for applying impulses to said input circuit, said last means comprising a condenser in parallel with a gas discharge device, having an anode, a cathode and a control electrode, said anode and said cathode being connected in said input and said output circuit, a

load connected in said output circuit, means for rendering said unit vacuum tubes cyclically operable in accordance with said variable current, means for impressing a different signal on each of said unit vacuum tubes, 9. receiving station and means at said receiving station for receiving said signal.

8. In a multiplex signaling system, with a plurality of channels, a generator 01' variable current, said generator comprising a vacuum tube having an input and output circuit, means for supplying a voltage to said input circuit, said means comprising a gas discharge device and condenser in parallel, said device having an anode, a cathode, and a control electrode, said anode and said cathode being connected in said input and said output circuit, a vacuum tube choke connected in said output circuit, means for generating a synchronizing voltage, means for controlling the potential of said control electrode with said synchronizing voltage, means for rendering each of said channels operable at difierent portions 01 the cycle oi. said variable current, and means-for controlling each of said channels with a different signal.

9. In a multiplex signaling system, with a plurality of channels, cyclically operable transmitting means, for each of said channels, cyclically operable receiving means for each -oi-' said channels, pulse generating means, said pulse generating means comprising a vacuum tube having an input and an output circuit, a gas discharge device in parallel with a condenser in series with a source of current and an impedance in said input circuit, a source ofvoltage and the primary of a transformer in said output circuit, an unidirectional current conductor in series with the escapee secondary of said transformer, means for storing energy in the core of said transformer during the'interval said gas discharge device is nonconductive, and means for releasing said energy in the form of a high voltage pulse when said gas 1 discharge device becomes conductive, and means for synchronizing said receiving means with said transmitting means with said high voltage pulse.

of. said grid leak tube, a receiving station, and means at said receiving station for translating voltage variations across said last mentioned load into signals.

10. In a multiplex signaling system with a plurality of channels, cyclically operable transmitting means for each of said channels, said means comprising a vacuum tube having an anode, a cathode, and a control electrode, cyclically operable receiving means for each of said channels, means for synchronizing said transmitting and receiving means, means for-impressing difierent signals on each of said transmitting means, means for amplifying said sig-' 13. In a multiplex signaling system, cyclically operable units at a transmitting station, cyclically' operable units at a receiving station, means for synchronizing said units at said transmitting and receiving stations, means for simultaneously changing the sequence of operability 01 said units at both of said stations to a different sequence, said last means comprising a tape at each ofsaid stations and means for synchronizing the movements of, said tape at each of said stations.

14. In asignaling system, a transmitting station, a receiving station, cyclically operable, units at each of said stations, means for synchronizing said units at said transmitting and receiving nals, said last means comprising a vacuum tube amplifier having an input and output circuit, a plate, filament and grid, said anode and said cathode of said first mentioned vacuum tube of each of said channels being connected in parallel in said input and output circuits, a-1oad in said output circuit, a' second vacuum tube amplifier having a plate, filament and grid, a, voltage dropping resistance connecting the grid of said,

second amplifier to the plate of said first amplifier, a vacuum tube grid leak connecting saidgrid and filament of said second amplifier, said vacuum tube grid leak comprising a vacuum tube having a plate, grid and filament, the plate of said vacuum tube grid leak being connected to said grid of said second amplifier, the filament of said grid leak tube being connected to said filament of said second amplifier through a r'esistelectrode, means for impressing a different signal on the control electrode of each of said vacuum tubes, means for amplifying said signals, said last means comprising an amplifier vacuum tube having an input and an output circuit, a load connected in said output circuit, means for applying said signals to said input circuit, said last means comprising the parallel connection of said anode and said cathode of each of said unit vacuum tubes in said input and said output circuits, means for synchronizing said commutators, and means at said receiving station for translating said voltages across said load into signals.

12. In a signaling system, means for producing a plurality of pulses of the same polarity, a first vacuum tube amplifier having an anode, a cathode, and a control electrode, a load connected in said anode circuit, means for impressing said pulses on said control electrode, a second vacuum tube amplifier having a plate, grid, and filament, a load in the plate circuit of said second ampli fier, said grid being connected to said anode through a voltage dropping resistance, a grid leak comprising a vacuum tube having an anode, a cathode and a control electrode, said anode of said grid leak tube being connected to said grid, said cathode of said grid leak tube being connected to said filament through a resistance common to said anode and control electrode circuits 7 stations, means for varying the sequence of operability of said units at both of said stations to a new sequence, said last means comprising similar .tapes at each ofsaid stations, .means for synchronizing the movements of said tapes, and

means for varying said sequence in accordance with a record on said tapes.

15. In'a multiplex signaling system, a transmitting station, a receiving station, an electronic commutator at each of said stations, said commutators comprising commutator unit vacuum tubes, each of said vacuum tubes having a plurality of grids, means for synchronizingsaid commutators at said transmitting and receiving 9 stations, said synchronizing means comprising means for generating a voltage at each oi saidc stations, means for applying said voltage to said grids of each of said vacuum tubes to tend to produce a positive potential on. one of said grids of each tube, and a negative potential on another of said grids of each of said tubes, means for biasing said grids of corresponding vacuum tubes of said commutators to render said corresponding units operable simultaneously, means for changing the sequence of operability of said vacuum tubes to a new sequence, said last means comprising ,a plurality of sources of voltage, a

plurality of potentiometers across each or said sources of voltage for biasing said grids in difierent magnitudes, each of said potentiometers comprising a photo-electric cell and a resistance,

a photo-electric record at each of said stations,"

means for synchronizing the movements of said records, and means for changing the bias on each of said grids in accordance with said records.

16. In a signaling system,- a transmittingstation, a receiving station, an electronic comm1i--- tator at each 'of said stations, each of said commutators comprising a plurality of commutator unit vacuum tubes, means for synchronizing said commutators, to render corresponding vacuum tubes operable simultaneously, means for chang-' ing the sequence of operation of said unit vacuum tubes to a new sequence, said last means-com prising a plurality of photo-electric cells, each of said cells controlling the instant of operability, of a difierent one of said tubes, a photo-electric record at each of said stations, means for synchronizing the movements of said records, and means for. controlling the impedance of said photo-electric cells in accordance with light received from said records.

17. In a multiplex signaling system, a transmitting station, a receiving station, an electronic commutator at each of said stations, said electronic commutator comprising unit vacuum tubes, each of said vacuum tubes having a plu- 6 r a,soo,ees

rality oi. grids, means for synchronizing said commutators, means for generating a variable voltage, said means comprising a gas discharge device in parallel with a condenser, in series with a source oi voltage and a load, said load comprising a plurality of vacuum tube chokes, each of said chokes comprising a high vacuum tube with an anode, a cathode, and a control electrode, a resistance common to the circuit of said anode and the circuit of said control electrode, means for impressing a voltage across one of said chokes on one of said grids, to tend to produce a positive potential on a first or said grids, means for impressing the voltage across the other or said chokes on the other of said grids, to tend to produce a negative potential on another of said grids,

and means for biasing said grids to render each or said vacuum tubes conductive to diiierent magnitudes of said variable voltage.

18. In a multiplex signaling system, a transmitting station, a receiving station, an electronic commutator at each ot-said stations, each of chronizing a receiver with a transmitter com-.

said commutators comprising a plurality of unit vacuum tubes, each having a plurality of grids, means tor generating a variable voltage, said means comprising a gas discharge device in parallel with a condenser, in series with a source of voltage and a plurality or load resistances, means for applying the voltage across one of said resistances to one or said grids, thereby causing said one grid to tend to assume a positive potential, means 101- applying the voltageacross the other or said resistances to theother or said grids, thereby causing said other grid to tend to assume a negative potential, means for biasing said grids to render each or said vacuum tubes conductive at diiierent values of said variable prising: a vacuum tube having an input and an output circuit, a gas discharge device in parallel with a condenser in said input circuit, a source of voltage and the primary 0! a transformer in said output circuit, means for storing energy in the core of said transformer during the interval said gas discharge device is nonconductive, means for releasing said energy in the form or a high voltage pulse when said gas discharge device 'becomes conductive, and means for synchronising said receiver with said transmitter with said pulse. 1 OLIVER T. FRANCIS. 

